# Index

Index (pl.: indexes or indices) may refer to:

## Arts, entertainment, and media
### Fictional entities

* Index (A Certain Magical Index), the titular character of the light novel series A Certain Magical Index
* The Index, an item on the Halo Array in the Halo video game series

### Periodicals and news portals

* Index Magazine, a publication for art and culture
* Index.hr, a Croatian online newspaper
* index.hu, a Hungarian-language news and community portal
* The Index (Kalamazoo College), a student newspaper
* The Index, an 1860s European propaganda journal created by Henry Hotze to support the Confederate States of America
* Truman State University Index, a student newspaper

### Other arts, entertainment and media

* The Index (band)
* Indexed, a Web cartoon by Jessica Hagy
* Index, album by Ana Mena

## Business enterprises and events

* Index (retailer), a former UK catalogue retailer
* INDEX, a market research fair in Lucknow, India
* Index Corporation, a Japanese video game developer

## Finance

* Index fund, a collective investment scheme
* Stock market index, a statistical average of prices of selected securities

## Places in the United States

* Index, Arkansas, an unincorporated community
* Index, Kentucky, an unincorporated community
* Index, Missouri, a ghost town
* Index, New York, a hamlet in Hartwick and Otsego, New York
* Index, Virginia, an unincorporated community
* Index, Washington, a town
* Index, West Virginia, an unincorporated community

## Publishing and library studies

* Index (publishing), an organized list of information in a publication
* Index (typography), a hand- or fist-shaped punctuation mark
* Bibliographic index, a regularly updated publication that lists articles, books, or other information items
* Citation index
* The Index, colloquial name for The List of Media Harmful to Young People (Germany)
* Index card, used for recording and storing small amounts of data
* Index Librorum Prohibitorum, a list of publications which the Catholic Church censored
* Index on Censorship, a publishing organization that campaigns for freedom of expression, or its magazine of the same name
* Subject indexing, describing the content of a document by keywords
* Thumb index, a round cut-out in the pages of a publication
* Web indexing, Internet indexing

## Science, technology, and mathematics
### Computer science

* Index, a key in an associative array
* Index (typography), a character in Unicode, its code is 132
* Index, the dataset maintained by search engine indexing
* Array index, an integer pointer into an array data structure
* BitTorrent index, a list of .torrent files available for searches
* Database index, a data structure that improves the speed of data retrieval
* Index mapping of raw data for an array
* Index register, a processor register used for modifying operand addresses during the run of a program
* Indexed color, in computer imagery
* Indexed Sequential Access Method (ISAM), used for indexing data for fast retrieval
* Lookup table, a data structure used to store precomputed information
* Site map, or site index, a list of pages of a web site accessible to crawlers or users
* Web indexing, Internet indexing
* Web server directory index, a default or index web page in a directory on a web server, such as index.html

### Economics

* Index (economics), a single number calculated from an array of prices and quantities
** Price index, a typical price for some good or service

### Mathematics and statistics

* Index, a number or other symbol that specifies an element of an indexed family or set
* Index, an element of an index set
* Index, the label of a summand in Σ-notation of a summation

#### Algebra

* Index of a subgroup, the number of a subgroup's left cosets
* Index, the degree of an nth root
* Index of a linear map, the dimension of the map's kernel minus the dimension of its cokernel
* Index of a matrix
* Index of a real quadratic form

#### Analysis

* Index, the winding number of an oriented closed curve on a surface relative to a point on that surface
* Diversity index, a measure of distribution or variety in fields such as ecology or information science
* Index of a vector field, an integer that helps to describe the behaviour of a vector field around an isolated zero

#### Number theory

* Index, or the discrete logarithm of a number

#### Statistics

* Index (statistics), a type of aggregate measure
** Scale (social sciences), a method of reporting data in social sciences, sometimes called an index

### Other uses in science and technology

* Dental indices, standardized scoring systems for tooth problems
* Indexicality, in linguistics, the phenomenon of a sign pointing to some object in the context in which it occurs
* Indexing (motion), in mechanical engineering and machining, movement to a precisely known location
* Refractive index, a measurement of how light propagates through a material
* Valve Index, a virtual reality headset

## Other uses

* INDEX, earlier name for the Reimei satellite
* Index:, a Danish nonprofit organization that promotes Design for Life
* The Index (Dubai), a skyscraper
* Index (crater), a Moon crater